I'm not a fan of them anyway, but this one looks too short IMO.
There's probably a reason the LMP cars have such long fins.
Reason: Rules. They were added to help prevent the yaw conditions that resulted in blowovers, and to disrupt the crude aerofoil shape the cars have when sideways to help prevent said blowovers.
Haha yeah, I actually made mine a fair bit larger than the design i was given. This one seems mostly cosmetic anyway, the massive sails on LMP1s usually are the weight bearing structure of the rear wing too which sort of ensures they are huge.
The fin on the rear bodywork is actually not directly connected to the rear wing; the wing support is just the last few inches of that fin, which is connected to the gearbox or otherwise to the chassis, and not the rear bodywork. The fin itself is the size that it is because the rules say so, mostly. They are typically a big larger than the minimums specified in the rules, but that's mostly for a more continuous shape for aero (and likely aesthetic) reasons. It has zero structural impact to anything.